Why: Several factors determined the cost-benefit-ratio of war chariot. This ratio changed with different tempo in different regions, as different factors became differently important. To list the most important:
- the breeding of horses changed significantly over the centuries, horses became taller and stronger, so the cost-benefit-ratio improved towards cavalry (single horsemen)
- the chariots became such a powerful weapon because of their ability to surround fastly small infantry troops and shoot arrows and spears on them (remember the scene in the Gladiator Movie). It was a hard to counter this attrition tactics for the infantry soldiers. But this shifted with ongoing time, as shields and armour of infantry were improved and the infantry number became on average much larger. A enemy with own strong cavalry could easily attack the chariots, as a single horse is more nimble than a chariot with 2-3 horses.
- landscape/battle field changed, chariots worked only on flat territories, again cavalry was more flexible here.
When: As said, the cost-benefit-ratio became worse at different times, also the knowledge of how to counter the typical strategies of chariots perfectly.
- the military importance ceased in the 4th century BC
However, by this time cavalry was far more effective and agile than the chariot, and the defeat of Darius III at the Battle of Gaugamela (331 BC), where the army of Alexander simply opened their lines and let the chariots pass and attacked them from behind, marked the end of the era of chariot warfare.
- The last mention of chariotry in battle seems to be at the Battle of Mons Graupius, somewhere in modern Scotland, in AD 84. From Tacitus (Agricola 1.35 -36)
- thenceforards chariots were mainly used for races (as in Ben Hur Movie)
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